1. Field of the Invention
The present invention relates to a control system for an internal combustion engine, and particularly to a control system which calculates a target intake air amount of the engine, and performs an intake air amount control according to the target intake air amount and an ignition timing control.
2. Description of the Related Art
Japanese Patent Publication No. 2929895 (JP-'895) discloses an idling rotational speed control apparatus for an internal combustion engine. According to this control apparatus, a correction air amount for correcting the intake air amount is calculated so that an idling rotational speed coincides with a target rotational speed, and the correction air amount is controlled to be increased as the retard correction amount of the ignition timing increases. This control is performed since the engine output torque decreases as the retard correction amount of the ignition timing increases. The control response performance of the idling rotational speed is secured by increasing the intake air amount when the retard correction of the ignition timing is performed.
In relation to the retard correction of the ignition timing, it is necessary to take the following points into consideration when calculating the target intake air amount according to the target output torque of the engine and performing the intake air amount control so that the actual intake air amount coincides with the target intake air amount. When the engine temperature or the intake air temperature is high, or when the knocking may easily occur, the ignition timing is corrected in the retard direction. Accordingly, it is necessary not only in the idling condition as shown in JP-'895 but also in the normal operating condition other than the idling condition, to set the target intake air amount in consideration of the ignition timing setting when the engine output torque is controlled to the target torque. However, if the intake air amount changes, the intake pressure will change and the retard correction amount of the ignition timing will also change. Further, when the retard correction amount changes, the engine output torque changes. Accordingly, it is necessary to change the target intake air amount. Therefore, according to the simple control as shown in JP-'895, the engine output torque cannot be controlled to appropriately follow the target output torque when the target output torque changes.